Carrot Fit app passes judgment. / Carrot Fit

by Jolie Lee, USA TODAY Network

by Jolie Lee, USA TODAY Network

The judgmental weight-loss app motivates with a tough-love approach to transform your "flabby carcass," according to the app's introduction.

"You're not going to get the butt you want by sitting on it," the app says if you gain weight. Or, "Suck it up so one day you won't have to suck it in."

But the National Eating Disorders Association says the app is an example of body shaming.

"People who are criticized for their size often engage in dangerous dieting behaviors that put them more at risk for disordered eating and, ultimately, eating disorders," said Lynn Grefe, president of NEDA, in a statement.

The app's developer, Brian Mueller, said the purpose of Carrot Fit is not to make people feel bad but to have a "fun" way for people to lose weight "so it doesn't suck so bad."

The app, which costs $1.99 on iTunes, insults or compliments you after you type in your weight - all in a sarcastic style.

The Carrot personality is based on the characters of HAL 9000 in 2001: A Space Odyssey and GLaDOS in the Portal video game, Mueller said in an interview with USA TODAY Network.

The character is also "a combination of my mom, my sister and my wife," Mueller said. "We make fun of each other a lot."

The app will say encouraging things if you get closer to your goal. If you lose weight, the app delivers lines like, "You are officially my favorite meat bag," or "You could be a part-time model."

Mueller has introduced two other Carrot apps - a to-do list and an alarm clock. Both apps are based on Carrot's snarky personality as a tool to motivate users.

"You get attached to the character and you want to impress her and make her proud of you," Mueller said.

Since it was introduced on Thursday, Carrot Fit has been downloaded tens of thousands of times, he said.

"My obedience knows no bounds to my Carrot Overlord. My one wish is to become less like a meat bag, and more like an exemplary servant," said one of the app's reviewers on iTunes, who rated the app five out of five stars.

But another reviewer gave it one star, saying, an "app that can verbally abuse you if you gain a little weight is uncalled for even if it is supposed to be funny."

Research has found there are negative effects of weight discrimination.

Shaming people who view themselves as overweight can make them feel stressed, and that stress in turn leads to a desire to eat more, said Brenda Major, a professor in the Department of Psychological and Brain Sciences at University of California Santa Barbara, in an interview with USA TODAY Network.

But people who do not view themselves as overweight actually feel more in control of their weight when exposed to weight stigma, said Major, whose study was published last month in the journal Social Psychological and Personality Science.

"It makes me think the people who design these apps aren't fat or at least feel in control of their weight," she said.

Another study, a survey from Florida researchers, asked 6,000 American men and women age 50 and older if they experienced weight discrimination. Of those who did, the overweight individuals were more likely to become obese, and the obese individuals were more likely to stay obese four years later, according to the findings published in July 2013 in the journal PLOS ONE.

In much of the research on weight bias and weight gain, "there's a real interpersonal aspect of it," said Angelina Sutin, the study's lead researcher and an assistant professor in the Department of Medical Humanities and Social Sciences at Florida State University College of Medicine.

But it's unclear if discrimination coming from a device has the same negative impact.

"From the research on the humans doing it to each other, it's not really a good motivator," Sutin said in an interview with USA TODAY Network. "Whether it's your phone saying it to you, who knows?"